On 15/04/12 2:48 PM, Frank Warmerdam wrote:
On 12-04-12 05:53 PM, ahbrown wrote:
Hi,
I am wondering why there is such a large difference in the time to
convert a
large O(250MB) Jpeg2000 image to GeoTiff format in comparison with
conversion to other formats (e.g. jpeg, png)?
I am using the Kakadu Jpeg2000 driver. With a 43221 x 36021 Jpeg2000
image.
Results of timed conversions are as follows:
Using RasterIO directly (via the Java wrapper) the conversion takes
around 6
seconds.
Adam,
Many drivers implement the CreateCopy() rather than Create() method.
In these
cases the input dataset is passed to the output driver and they pull
data in
whatever way is convenient.
The PNG and JPEG drivers are "CreateCopy" drivers and likely request data
one scanline at a time. In this situation the JP2KAK driver actually
gets
asked for the data in moderate sized tiles which turns out not to be very
efficient for the Kakadu library as there is a high setup cost for each
windowed read.
The GeoTIFF format support Create(), so gdal_translate is able to more
closely manage the chunking of reads and writes and tries to do it in
large chunks. The JP2KAK driver handles large reads through IRasterIO()
as single windowed reads which are more efficient than the smaller tile
reads.
So I think the bulk of the difference in performance is related to
different
IO strategies that apply against the JP2KAK driver. The variation
between
JPEG and PNG times is likely different costs on the compression side.
PS. it appears posts through nabble do not preserve some components, like
the fixed font timings text. I encourage direct use of the mailing list
for posts.
Best regards,
Hi Frank and Chaitanya,
Thanks for the quick response.
What doesn't make sense to me is that I can perform the same JP2->PNG
translation benchmarked below in a little over 6 seconds using the GDAL Java
wrappers.
Most of this is spent in the read/subsample operation. The write to the 200x200
png takes only 20 ms.
So gdal_translate is adding 8-12s of overhead somewhere.
I've posted the timings again below as they were stripped out from the original
post:
time gdal_translate -of GTiff -outsize 200 200 master_original.jp2
master_original.tif
real 0m2.325s
time gdal_translate -of JPEG -outsize 200 200 master_original.jp2
master_original.jpg
real 0m18.317s
time gdal_translate -of PNG -outsize 200 200 master_original.jp2
master_original.png
user 0m14.588s
GDAL Java wrapper (same JP2 to 200x200 PNG): approx 6s
Regards,
Adam
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